A video or video stream is a collection of sequential image frames. Occasionally, due to any of a number of reasons, artifacts may appear in portions of a video frame. Sometimes artifacts are produced by dropouts caused when a video is read from an imperfect portion of video tape. Imperfections may be caused by defects in the magnetic tape particles, tape aging, damage to the tape, dirt, or worn video heads, for instance. In other cases artifacts may appear that were not caused by tape defects, but could be caused by other means, and even in completely digital systems.
As used herein, artifacts may be considered to be a group of affected pixels of a video frame. The group is typically rectangular in shape, and the pixels within structured artifacts form patterns. The patterns may include, for example, alternating horizontal or vertical lines, or alternating pixels in a 2-D array pattern similar to a checkerboard, or their variants. FIG. 1 illustrates example structured artifacts. As seen in FIG. 1, a frame 5 includes multiple artifacts 8, a specific example of which is identified as an area 10. Typically the frame 5 would be filled with image data, and a few or several artifacts 8. As seen in the exploded section, an artifact 15 consisting of alternating horizontal lines may fill the area 10. This artifact may have been caused by a tape dropout, or by other means as described above.
FIG. 2 illustrates other artifact shapes that may fill any of the artifacts 8 of FIG. 1. For example artifact shapes may include vertical lines 25, a series of individual pixels 35, or a combination of vertical and horizontal lines and pixels, as illustrated by 45, 55, 65, and 75. The artifact patterns generally have a noticeable contrast when compared to surrounding unaffected pixels.
Small artifacts may go completely unnoticed by the viewer upon playback because standard error correction techniques may compensate for the artifacts. Large artifacts, however, are noticeable by viewers. Sometimes artifacts appear in a number of successive frames. Artifacts negatively affect the viewer experience by distracting the viewer from the content of the video itself.
Embodiments of the invention address these and other limitations of the prior art.